Some semiconductor devices, such as some metal on silicon (MOS) transistors in memory devices, are fabricated using silicon-on-insulator (SOI) substrates. SOI substrates can improve operational characteristics of some semiconductor devices, such as by reducing parasitic capacitance and/or other undesirable conditions in those devices. The structure of a SOI substrate can include a silicon film that is insulated from a bulk semiconductor substrate by an insulating film therebetween.
In a transistor device that is formed on the insulated silicon film of a SOI substrate, electron ionization in the insulated silicon film near the transistor's drain may cause holes to accumulate. Accumulation of holes may decrease the potential barrier of the transistor's source and may result in a decrease in the threshold voltage of the transistor (floating body effect) and an increase in drain current (kink effect).
As integration densities of semiconductor devices using SOI substrates continue to increase, the accumulation of holes in the SOI substrates may have more undesirable effects on the operation of the associated devices.